Medical devices are often assembled from components formed from many different materials. It often is necessary to apply a coating of a lubricant to one or more of the components so that a component of one material will readily slide against a component of another material. Examples of this type of application are catheters with guidewires, over-the-needle catheters, syringe plunger stoppers within syringe barrels, needles for penetration of blood collection tube stoppers and the like. In other medical device applications, a lubricant is applied to a device to ease its penetration into the body. Examples of these applications are surgical blades, hypodermic needles, peripheral venous catheters and the like.
In all of these medical device lubrication applications, there are strict requirements on the amounts of lubricant, the uniformity of the application and a need to avoid contamination of the device with foreign material other than the lubricant. A further requirement on application of lubricant results from the high volume production requirements often resulting in the use of high speed assembly equipment. Thus, any lubricant application must be precise and compatible with high volume production.
Currently, a commonly used lubricant for medical devices is "silicone," i.e., polydimethylsiloxane having a Brookfield viscosity between about 1,000 and 1,000,000 centistokes (cs). For some applications, the silicone is applied "neat," i.e., without solvent. An example of neat application of silicone to syringe plunger stoppers is disclosed in U.S. Pat. No. 5,207,293 to Eden et al. This patent discloses a method and apparatus for lubricating syringe stoppers by moving the stoppers between a pair of wheels that are positioned partially in a reservoir containing lubricant so that, with rotation of the wheels, lubricant is transferred to the stoppers.
Another commonly used neat application method is tumbling a measured quantity of small parts, such as stoppers, with a measured quantity of lubricant so that the parts acquire a coating of the lubricant.
Silicone lubricant also may be sprayed onto the parts either neat or in a carrier solvent. Neat spraying has been found to work well for interior surfaces such as inside syringe barrels. Solvent based dipping or spraying is commonly used for coating hypodermic needles and percutaneous catheters. Chlorofluorcarbon solvents have proven to be very satisfactory for the delivery of silicone onto medical devices because they are non-toxic, non-flammable, inert, evaporate rapidly without leaving residue and are available in very high purity. Unfortunately, because of the belief that chlorofluorcarbon solvents are responsible for destruction of ozone in the upper atmosphere, most commonly used chlorofluorocarbon solvents will no longer be available. Alternate solvents such as hydrocarbons are flammable, and aqueous based systems generally are not practical for silicones.
When silicone lubricant is applied to a device in a solvent, the device is generally sprayed with or dipped in a dilute solution of the silicone containing solvent. In these application techniques, the solution with a low concentration of lubricant is generally present in excess. The dilute solution is often sprayed or flowed over the device being coated, in excess of the amount required to coat it. Thus, as long as this excess is maintained and monitored, there is substantial confidence that the medical devices have a substantially uniform coating of at least the minimum desired quantity. When the silicone is applied directly or "neat," there is not the same level of confidence that the desired amount of silicone is being applied. The actual amount of silicone lubricant applied to each individual device, such as an intravenous catheter or hypodermic needle is very small.
Two recent U.S. patent applications, commonly assigned with the present application, Ser. Nos. 08/509,393, abandoned, and 08/509,395, pending, disclose the neat application of polydimethylsiloxane to medical devices. An example given the in these referenced disclosures is the application of 12,500 cs. polydimethylsiloxane to 14 gauge intravenous catheters. In the examples, the referenced applications disclose that about 0.3.+-.0.075 mg is applied to each individual catheter. Polydimethylsiloxane is a clear water white liquid. It is available in a wide range of viscosities ranging from about 50 cs. to about 1,000,000 cs. Because of the physical characteristics of polydimethylsiloxane and the small amount applied to each catheter, it is difficult to differentiate between a lubricated catheter and an unlubricated catheter by visual comparison. Thus, it is almost impossible to determine visually and rapidly if an individual catheter has the desired uniform coating. Since these catheters are medical devices, they must be manufactured according to Good Manufacturing Practices (GMP) as defined by the Food and Drug Administration. An important aspect of GMP is developing the ability to validate and to monitor production processes.
One way to determine the amount of silicone on a catheter is to carefully weigh identified catheters, feed them through the process and then reweigh them to determine the silicone loading. This technique allows a determination of the gross amount of polydimethylsiloxane on an individual catheter, but it is considered a "destructive" test, i.e., the identified catheter generally cannot be put back into the process. Additionally, with weighing, no determination can be made of the uniformity of the application. Another destructive method involves washing the polydimethylsiloxane off the catheter with a solvent, evaporating the solvent and weighing the residual polydimethylsiloxane. Again, washing does not address the need to determine if the application is uniform.
Because of the GMP requirements that the production of medical devices be validated and controlled, there is a need for a non-destructive method to monitor the application of lubricants to their surfaces. Additionally, since many medical devices are single-use and produced in large volumes, if the monitoring method was relatively inexpensive and compatible with high volume, high speed manufacturing processes, an additional benefit to the art of medical device manufacture would be realized. Materials, a method and a system for visualization of polydimethylsiloxane on the surface of a medical device are disclosed below.